1. Field of the Invention
The invention relates to an interface for damping or isolating mechanical vibrations by means of a plurality of energy converter systems. Such interfaces are used, for example, for damping vibrations in the field of general machine engineering, the automotive industry, the construction industry or the aerospace industry.
Dynamic mechanical interference in the form of vibrations which are excited, for example, by the operation of assemblies (for example power supply assemblies) or by other ambient conditions, are produced in machines, vehicles and similar modules. The frequencies of these vibrations extend into the relatively high frequency acoustic range and bring about undesired dynamic and/or acoustic effects locally at the location where the interference is produced or applied, or further away after transmission over mechanical load paths. This results in losses of comfort, safety problems, damage to components owing to structural fatigue, shortened service life, reduced functionalities etc.
2. Description of the Related Art
What is referred to as material damping, in which the mechanical energy of the vibration is converted directly into thermal energy, is frequently used to damp or isolate mechanical vibrations. Examples of this are elastic or viscoelastic damping systems.
In addition, measures which are based on other energy converter systems are increasingly used. These energy converter systems generally convert mechanical energy into electrical energy and vice versa. Both effects are used to damp mechanical vibrations. The distinction is generally made here between active, semiactive and passive vibration dampers.
In the case of passive and semiactive vibration damping, the mechanical energy of the vibrations is firstly converted into electrical energy using an electric/mechanical energy converter (for example a piezoceramic). This electrical energy is then dissipated, i.e. converted into thermal energy, in a passive electrical circuit (e.g. an ohmic resistor) in the case of passive vibration damping, or diverted using an active electric circuit (for example electric damper) in the case of semiactive vibration damping. Such systems are described, for example, in N. W. Hagood and A. von Flotow: Damping of Structural Vibrations with Piezoelectric Materials and Passive Electrical Networks, Journal of Sound and Vibration 146 (2), 243 (1991).
In the case of active vibration isolation, at least one actuator system is connected between an interference source (base side) and a connection side. In this context, “actuator” refers to an energy converter which, for example, can convert electrical signals into mechanical movements, for example a piezoactuator or a pneumatic actuator. What is decisive is that the characteristic (for example extent) of the actuators can be varied in a controlled fashion by means of an actuation signal. An example of a system for active vibration isolation using actuator elements is disclosed in U.S. Pat. No. 5,660,255. Actuator elements and a small additional mass are interposed between a base housing and a useful load which is to be isolated. Sensors which record the displacement of the small mass are mounted on said small mass. An actuation signal for the actuator elements is generated from the displacement using an electronic closed-control circuit and an external electrical energy source. The actuator elements are actuated in such a way that the vibration movement at the location of the useful load is largely eliminated.
FIG. 1 shows a satellite as an example of active isolation of interference sources and sensitive components which should be protected from mechanical interference. The satellite contains internal interference sources 1, for example mechanical coolers, motors etc. Mechanical interference from these interference sources 1 is damped by active elements 2, 3, 4 so that the interference from the interference sources 1 does not act on the sensitive components 5 (cameras, reflectors, etc.) via transmission paths 3, 4.
In addition to the use for active, passive and semiactive vibration damping, the electric/mechanical energy converters can often simultaneously be used as actuating elements for mechanical positioning of a useful load. This may be done, for example, by virtue of the fact that an annular arrangement of a plurality of actuators is integrated into a vibration-damping interface which can bring about, for example, selective tilting of a structure with respect to a base. Such a system is disclosed, for example, in DE 195 27 514 C2.
For structural reasons, actuator systems are frequently operated in practice with a preload. This is frequently a mechanical preload in the form of compressive loading or tensile loading on the actuator system. For example in the case of piezoactuators in which extension beyond the length at rest (i.e. length of the actuator without voltage applied) would lead to mechanical damage to the actuator, operation without preloading is in practice inappropriate or not possible. However, the structural implementation of a device for exerting a preload presents problems, in particular in the case of the actuator or actuators whose extension direction extends parallel to the force (for example the force of the weight) exerted by the useful load, and has a frequently negative effect on the effectiveness of the actuator. U.S. Pat. No. 5,660,255 does not disclose a satisfactory solution to this problem.
DE 195 27 514 C2 discloses an interface for reducing vibrations in structural dynamic systems in which vibration insulation occurs between a structure-side component and a base-side component by means of a plurality of actuators which have a main direction. Pressure pretensioning on the actuators is ensured by anti-fatigue bolts between the base-side component and the structure-side component. However, such a rigid mechanical connection between the base-side component and the structure-side component has the disadvantage that as a result a bridge is provided via which vibrations can propagate from a base-side interference source to the structure-side component.